Infusion pump with a capacitive displacement position sensor

ABSTRACT

Various methods and devices are provided for an electrokinetic infusion pump. In one embodiment of the invention, the infusion pump includes an infusion pump module, which can be configured to dispense an insulin containing infusion liquid, and an electrokinetic engine. The infusion pump module includes a capacitive displacement position sensor configured for sensing a dispensing state of the infusion pump module. The infusion pump module can include an infusion module housing and the electrokinetic engine can include a moveable partition. The capacitive displacement sensor includes a first capacitive plate disposed on the moveable partition and a second capacitive plate disposed on the infusion module housing. The capacitive displacement sensor is configured for measuring capacitance between the first capacitive plate and the second capacitive plate and can send a feedback signal to a closed loop controller that is indicative of the capacitance between the first and second capacitive plates.

FIELD OF THE INVENTION

The present invention relates, in general, to a medical devices and systems and, in particular, to infusion pumps, infusion pump systems and associated methods.

BACKGROUND

Electrokinetic (EK) pumps provide for liquid displacement by applying an electric potential across a porous dielectric media that is filled with an ion-containing electrokinetic solution. Properties of the porous dielectric media and ion-containing solution (e.g., permittivity of the ion-containing solution and zeta potential of the solid-liquid interface between the porous dielectric media and the ion-containing solution) are predetermined such that an electrical double-layer is formed at the solid-liquid interface. Thereafter, ions of the electrokinetic solution within the electrical double-layer migrate in response to the electric potential, transporting the bulk electrokinetic solution with them via viscous interaction. The resulting electrokinetic flow (also known as electroosmotic flow) of the bulk electrokinetic solution is employed to displace (i.e., “pump”) a liquid. Further details regarding electrokinetic pumps, including materials, designs, and methods of manufacturing are included in U.S. patent application Ser. No. 10/322,083 (United States Published Application No. 2004/0074784) filed on Dec. 17, 2002, which is hereby incorporated in full by reference.

SUMMARY

The present invention provides various methods and devices for an electrokinetic infusion pump. In one embodiment, the electrokinetic infusion pump includes an infusion pump module, which can be configured to dispense a medicament or another treatment agent (e.g., an insulin containing infusion liquid), and an electrokinetic engine. The infusion pump module includes a capacitive displacement position sensor configured for sensing a dispensing state of the infusion pump module. The infusion pump module can include an infusion module housing and the electrokinetic engine can include a moveable partition. The capacitive displacement sensor includes a first capacitive element, such as a capacitive plate, disposed on the moveable partition and a second element, such as a capacitive plate, disposed on the infusion module housing. The capacitive displacement sensor is configured for measuring capacitance between the first capacitive element and the second capacitive element and can send a feedback signal to a closed loop controller that is indicative of the capacitance between the first and second capacitive plates. In one exemplary embodiment, the first capacitive plate and the second capacitive plate each have a width of approximately 10 mm and a length of approximately 20 mm. A gap between the first capacitive plate and the second capacitive plate can have a dimension in the range of approximately 10-1000 micrometers.

In another embodiment, the electrokinetic engine includes a moveable partition and the infusion pump includes an infusion housing, and the capacitive displacement sensor is a dual capacitive displacement sensor. The dual capacitive displacement sensor includes a first capacitive plate and a second capacitive plate disposed on the moveable partition and a third capacitive plate and a fourth capacitive plate disposed on the infusion housing. The first, second, third, and fourth capacitive plates are in operative electrical contact. An overlap between the second and fourth capacitive plate is constant and an overlap between the first capacitive plate and the third capacitive plate is dependent on a position of the moveable partition.

In another exemplary embodiment, an infusion pump system is provided that includes an infusion pump, for example, an electrokinetic pump, having a capacitive displacement position sensor and a closed loop controller. The infusion pump and closed loop controller are in operative communication and configured such that the closed loop controller can determine and control a dispensing state of the infusion pump based on a feedback signal received from the capacitive displacement position sensor. The infusion pump further includes an infusion pump module and an electrokinetic engine. The capacitive displacement sensor is configured for sensing a dispensing state of the infusion pump module. The infusion pump can be configured to dispense, for example, an insulin-containing infusion liquid.

The infusion pump module can include an infusion module housing and the electrokinetic engine can include a moveable partition. The electrokinetic engine can also include an electrokinetic supply reservoir that is at least partially collapsible. The capacitive displacement sensor can include a first capacitive plate disposed on the moveable partition and a second capacitive plate disposed on the infusion module housing, and the capacitive displacement sensor can be configured for sensing a dispensing state by measuring capacitance between the first capacitive plate and the second capacitive plate. In one embodiment, the first capacitive plate and the second capacitive plate each have a width of approximately 10 mm and a length of approximately 20 mm, and a gap between the first capacitive plate and the second capacitive plate has a dimension in the range of approximately 10-1000 micrometer.

In one embodiment, the electrokinetic engine includes a moveable partition and the capacitive displacement sensor is a dual capacitive displacement sensor that includes first, second, third, and fourth capacitive plates. The first, second, third, and fourth capacitive plates are in operative electrical contact and an overlap between the second and fourth capacitive plate is constant and an overlap between the first capacitive plate and the third capacitive plate is dependent on a position of the moveable partition.

Methods for the closed loop control of an infusion pump are also provided, and in one embodiment the method can include sensing a dispensing state of an infusion pump, for example, an electrokinetic infusion pump, with a capacitive displacement position sensor and signaling the sensed dispensing state of the infusion pump to a closed loop controller via a feedback signal. The closed loop controller determines the dispensing state of the infusion pump based feedback signal and controls the dispensing state of the infusion pump by sending command signals from the closed loop controller to an engine driving the infusion pump. These steps can be repeated to maintain control of the electrokinetic infusion pump.

Sensing the dispensing state can include sensing a position of a moveable partition of the electrokinetic infusion pump by the capacitive displacement sensor. Sensing the dispensing state can also include sensing the position of the moveable partition due to a change in overlap between capacitive plates of the capacitive displacement sensor. The dispensing state can be an infusion liquid displacement rate or an infusion liquid volume. The step of controlling the dispensing state can include controlling the dispensing state of an insulin containing infusion liquid. The capacitive displacement position sensor can be a dual capacitive displacement sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is an exploded schematic illustration of an electrokinetic infusion pump system with closed loop control according to an exemplary embodiment of the present invention in a first dispense state;

FIG. 2 is an exploded schematic illustration of the electrokinetic infusion pump system shown in FIG. 1 in a second dispense state;

FIG. 3 is a perspective illustration of an electrokinetic infusion pump system according to another exemplary embodiment of the present invention being manually manipulated;

FIG. 4 is a cross-sectional depiction of an electrokinetic infusion pump system according to a further exemplary embodiment of the present invention in a first dispense state;

FIG. 5 is a cross-sectional depiction of the electrokinetic infusion pump system shown in FIG. 4 in a second dispense state;

FIG. 6 is a perspective depiction of a portion of the electrokinetic infusion pump of the EK infusion pump system shown in FIG. 4;

FIG. 7 is a perspective depiction of a portion of the electrokinetic infusion pump of the EK infusion pump system shown in FIG. 5;

FIG. 8 is a perspective depiction of a portion of an electrokinetic infusion pump with capacitive displacement position sensors according to another exemplary embodiment of the present invention in a first dispense state;

FIG. 9 is a perspective depiction of the portion of an electrokinetic infusion pump shown in FIG. 8 in a second dispense state;

FIG. 10 is a schematic drawing depicting a capacitive plate configuration of the electrokinetic infusion pump shown in FIG. 8;

FIG. 11 is a schematic drawing depicting a capacitive plate configuration of the electrokinetic infusion pump shown in FIG. 9;

FIG. 12 is an electrical circuit schematic depicting the analog electric circuit formed by the capacitive displacement position sensor shown in FIGS. 8-11; and

FIG. 13 is a flow diagram illustrating a method for the closed loop control of an electrokinetic infusion pump according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the devices and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the devices and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present invention is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention.

Various exemplary methods and devices are provided for controlling the dispensing state of an infusion pump system. In particular, the methods and devices provide a capacitive displacement position sensor coupled with an infusion pump to control the dispensing of an infusion liquid from the infusion pump.

FIGS. 1-2 are exploded schematic illustrations of an electrokinetic (EK) infusion pump system 100 with closed loop control according to an exemplary embodiment of the present invention. FIG. 1. illustrates the EK infusion pump system 100 in a first dispense state, while FIG. 2 depicts the EK infusion pump system 100 in a second dispense state.

Referring to FIGS. 1 and 2, the EK infusion pump system 100 includes an electrokinetic (EK) infusion pump 102 and a closed loop controller 104. The EK infusion pump 102 can include a capacitive displacement position sensor (not shown in FIGS. 1 and 2). As is described in further detail below, the EK infusion pump 102 and the closed loop controller 104 are in operative communication such that the closed loop controller 104 can determine and control the dispensing state of the EK infusion pump 102 based on one or more feedback signals FB from the capacitive displacement position sensor. The EK infusion pump 102 and the closed loop controller 104 can be configured in a variety of ways. For example, the infusion pump 102 and the closed loop controller 104 can be entirely separate units, partially integrated (for example, predetermined components of the EK infusion pump 102 can be integrated within the closed loop controller 104), or a single integrated unit.

The EK infusion pump systems according to embodiments of the present invention, including the EK infusion pump system 100, can be employed to deliver a variety of medically useful infusion liquids such as, for example, insulin for diabetes; morphine and other analgesics for pain; barbiturates and ketamine for anesthesia; anti-infective and antiviral therapies for Acquired Immune Deficiency Syndrome (AIDS); antibiotic therapies for preventing infection; bone marrow for immunodeficiency disorders, blood-borne malignancies, and solid tumors; chemotherapy for cancer; dobutamine for congestive heart failure; monoclonal antibodies and vaccines for cancer, brain natriuretic peptide for congestive heart failure, and vascular endothelial growth factor for preeclampsia. The delivery of such infusion liquids can be accomplished via any suitable route including subcutaneously, intravenously or intraspinally.

The EK infusion pump 102 can also include an electrokinetic (EK) engine 106 and an infusion module 108. The EK engine 106 can include an electrokinetic (EK) supply reservoir 110, an electrokinetic (EK) porous media 112, an electrokinetic (EK) solution receiving chamber 114, a first electrode 116, a second electrode 118, and an electrokinetic (EK) solution 120 (depicted as upwardly pointing chevrons).

The pore size of the porous media 112 can be, for example, in the range of 100 nm to 200 nm. A person skilled in the art will appreciate that the porous media 112 can have any number of pores with any pore size that allows the appropriate amount of electrokinetic solution 120 to flow through it. Moreover, the porous media 112 can be formed of any suitable material including, by way of non-limiting example, Durapore Z PVDF membrane material available from Millipore, Inc. USA. EK solution 120 can be any suitable EK solution including, but not limited to, 10 mM TRIS/HCl at a neutral pH.

The infusion module 108 can include the EK solution receiving chamber 114 (which is also considered part of the EK engine 106), an infusion module housing 122, a movable partition 124, an infusion reservoir 126, an infusion reservoir outlet 128, and an infusion liquid 130 (depicted as dotted shading). Although the capacitive displacement position sensor of the infusion module 108 is not depicted in FIGS. 1 and 2, the feedback signal FB between the capacitive displacement position sensor and the closed loop controller 104 is shown.

The closed loop controller 104 can include a voltage source 132 and is configured to receive the feedback signal FB from the capacitive displacement sensor and to be in electrical communication with the first and second electrodes 116 and 118. The EK engine 106, the infusion module 108, and the closed loop controller 104 can be integrated into a single assembly, into multiple assemblies, or can be separate units.

During operation of the EK infusion pump system 100, the EK engine 106 provides the driving force for displacing (pumping) the infusion liquid 130 from the infusion module 108. To do so, a voltage difference is established across the EK porous media 112 by the application of an electrical potential between the first electrode 116 and the second electrode 118. This electrical potential results in an electrokinetic pumping of the EK solution 120 from the EK supply reservoir 110, through the EK porous media 112, and into the EK solution receiving chamber 114.

As the electrokinetic solution receiving chamber 114 receives the EK solution 120, the moveable partition 124 is forced to move in the direction of arrows μl, shown in FIGS. 1-2. Such movement is evident by a comparison of the first dispense state shown in FIG. 1 to the second dispense state shown in FIG. 2. As the moveable partition 124 moves in the direction of μl, the infusion liquid 130 is displaced (i.e., “pumped”) out of the infusion reservoir 126 and through the infusion reservoir outlet 128 in the direction of arrow μl. The EK engine 106 can continue to displace the EK solution 120 until the moveable partition 124 reaches a predetermined point near the infusion reservoir outlet 128, for example, a point just proximal of the infusion reservoir outlet 128, thereby displacing a predetermined amount (e.g., essentially all) of the infusion liquid 130 from the infusion reservoir 126.

It is evident from the description above and a comparison of FIGS. 1 and 2, that the second dispensing state represented by FIG. 2 is achieved by electrokinetically displacing (i.e., pumping or dispelling) a portion of the infusion liquid 130 that is present within the infusion reservoir 126 in the first dispensing state represented by FIG. 1.

The rate of displacement of the infusion liquid 130 from the infusion reservoir 126 is directly proportional to the rate at which the EK solution 120 is pumped from the EK supply reservoir 110 into the EK solution receiving chamber 114. The proportionality between the rate of displacement of the infusion liquid 130 (such as an insulin containing infusion liquid) and the rate at which the EK solution 120 is pumped can be, for example, in the range of 1:1 to 4:1. Furthermore, the rate at which the EK solution 120 is pumped from the EK supply reservoir 110 is a function of the voltage and current applied by the first electrode 116 and the second electrode 118 and various electro-physical properties of the EK porous media 112 and the EK solution 120 (such as, for example, zeta potential, permittivity of the EK solution and viscosity of the EK solution).

The features disclosed herein are applicable to a variety of electrokinetic infusion pump systems, including, for example, the electrokinetic infusion pumps and electrokinetic infusion pump systems of the type disclosed in U.S. patent application Ser. No. 11/532,587, filed Sep. 18, 2006, entitled “Electrokinetic Infusion Pump System,” which is incorporated herein in its entirety. In addition, features disclosed herein can be used in combination with electrokinetic infusion pump systems of the type disclosed in U.S. patent application Ser. No. 11/532,587, as well as with features of electrokinetic infusion pumps as disclosed in U.S. patent application Ser. No. 11/532,691, filed Sep. 18, 2006, entitled “Malfunction Detection With Derivative Calculation,” and U.S. patent application Ser. No. 11/614,211, filed Dec. 21, 2006, entitled “Malfunction Detection In Infusion Pumps,” both of which are likewise incorporated herein in their entirety.

Further details regarding EK engines, including materials, designs, operation and methods of manufacturing, are included in U.S. patent application Ser. No. 10/322,083 (United States Published Application No. 2004/0074784) filed on Dec. 17, 2002, which has been incorporated by reference. Although a particular EK engine is depicted in a simplified manner in FIGS. 1 and 2, any suitable EK engine can be employed in embodiments of the present invention including, but not limited to, the EK engines described in the aforementioned U.S. patent application Ser. No. 10/322,083 and EK engines that substitute a media with a microchannel(s) for the aforementioned porous media.

The capacitive displacement position sensor of EK infusion pump 102 is configured to sense (determine) the position of the moveable partition 124. Based on the sensed position of the moveable partition 124 (as communicated by feedback signal FB), the closed loop controller 104 can determine the dispensing state (e.g., the displacement position of the moveable partition 124 at any given time and/or as a function of time, the rate of displacement of the infusion liquid 130 from infusion reservoir 126, the rate at which the EK solution 120 is pumped from the EK supply reservoir 110 to the EK solution receiving chamber 114, and the volume of dispensed EK solution).

Based on such a determination of dispensing state, the closed loop controller 104 controls (i.e., can command and manage) the dispensing state by, for example, (i) adjusting the voltage and/or current applied between the first electrode 116 and the second electrode 118 or (ii) maintaining the voltage between the first electrode 116 and the second electrode 118 constant while adjusting the duration during which power is applied between the first electrode 116 and the second electrode 118. For example, by adjusting the voltage and/or current applied across the first electrode 116 and the second electrode 118, the rate at which the EK solution 120 is displaced from the EK supply reservoir 110 to the EK solution receiving chamber 114 and, therefore, the rate at which the infusion liquid 130 is displaced through the infusion reservoir outlet 128, can be accurately and beneficially controlled.

The closed loop control of EK infusion pumps described above beneficially compensates for variations that may cause inconsistent displacement (i.e., dispensing) of the infusion liquid 130 including, but not limited to, variations in temperature, downstream resistance, and mechanical friction.

The EK supply reservoir 110 can have a variety of configurations. In one embodiment, the EK supply reservoir 110 can be partially or wholly collapsible. For example, the EK supply reservoir 110 can be configured as a collapsible sack. Such collapsibility provides for the volume of the EK supply reservoir 110 to decrease as the EK solution 120 is displaced therefrom. Such a collapsible EK supply reservoir 110 can also assist in the prevention of undesirable bubble formation within the EK supply reservoir 110.

The infusion module housing 122 can also be configured in a variety of additional ways, and can be, for example, at least partially rigid to facilitate the movement of the moveable partition 124 and the reception of the EK solution 120 pumped from the EK supply reservoir 110.

The moveable partition 124 can be configured to prevent migration of the EK solution 120 into the infusion liquid 130, while minimizing resistance to its own movement (displacement) as the EK solution receiving chamber 114 receives the EK solution 120 pumped from the EK supply reservoir 110. The moveable partition 124 can, for example, include elastomeric seals that provide intimate, yet movable, contact between the moveable partition 124 and the infusion module housing 122. The moveable partition 124 can have a variety of configurations, such as, for example, a piston-like configuration, or the moveable partition 124 can be configured as a moveable membrane and/or bellows.

FIG. 3 is a perspective illustration of an electrokinetic (EK) infusion pump system 200 according to another exemplary embodiment of the present invention being manipulated by a user's hands (H). The EK infusion pump system 200 can include an electrokinetic (EK) infusion pump 202 and a closed loop controller 204.

The EK infusion pump 202 and the closed loop controller 204 can be handheld, and/or mounted to a user by way of clips, adhesives or non-adhesive removable fasteners. For example, the EK infusion pump system 200 can be configured to be worn on a user's belt, thereby providing an ambulatory EK infusion pump system. In addition, the closed loop controller 204 can be directly or wirelessly connected to a remote controller or other auxiliary equipment (not shown in FIG. 3) that provide analyte monitoring capabilities and/or additional data processing capabilities.

The EK infusion pump 202 and the closed loop controller 204 can include components that are essentially equivalent to those described above with respect to the EK infusion pump 102 and the closed loop controller 104. In addition, the closed loop controller 204 can include a variety of features, including a display 240, input keys 242 a and 242 b, and an insertion port 244.

The display 240 can be configured, for example, to display a variety of information, including infusion rates, error messages and logbook information. During use of the EK infusion pump system 200, and subsequent to the EK infusion pump 202 having been filled with infusion liquid, the EK infusion pump 202 can be inserted into the insertion port 244. Upon such insertion, operative electrical communication is established between the closed loop controller 204 and the EK infusion pump 202. Such electrical communication includes the ability for the closed loop controller 204 to receive a feedback signal FB from a capacitive displacement position sensor of the EK infusion pump 202 and operative electrical contact with first and second electrodes of the EK infusion pump 202.

One skilled in the art will recognize that an infusion set (not shown but typically including, for example, a connector, tubing, needle and/or cannula and an adhesive patch) can be connected to the infusion reservoir outlet of the EK infusion pump 202 and, thereafter, primed. As may be suitable for a particular infusion set, such attachment and priming can occur before or after EK infusion pump 202 is inserted into insertion port 244. After determining the position of a movable partition of EK infusion pump 202, voltage and current are applied across the EK porous media of EK infusion pump 202, thereby dispensing (pumping) infusion liquid.

FIG. 4 is a cross-sectional depiction of an electrokinetic (EK) infusion pump system 300 according to a further exemplary embodiment of the present invention in a first dispense state, while FIG. 5 depicts the EK infusion pump system 300 in second dispense state. FIG. 6 is a further perspective depiction of a portion of the EK infusion pump system 300 in the first dispense state of FIG. 4, while FIG. 7 is in the second dispense state of FIG. 5. As will be evident from the discussion below, the focus of FIGS. 6 and 7 is the capacitive displacement position sensor of the EK infusion pump system 300. Therefore, FIGS. 6 and 7 are further simplified versions of FIGS. 4 and 5 that serve to highlight the capacitive displacement position sensor.

Referring to FIGS. 4-7, the EK infusion pump system 300 includes an electrokinetic (EK) infusion pump 302 and a closed loop controller 304. As will be clear to one skilled in the art from the following description, the EK infusion pump 302 includes an integrated electrokinetic (EK) engine and infusion module (collectively element 306) and a capacitive displacement position sensor 307.

The integrated EK engine and infusion module 306 includes an electrokinetic (EK) supply reservoir 310, an electrokinetic (EK) porous media 312, an electrokinetic (EK) solution receiving chamber 314, a first electrode 316, a second electrode 318, and an electrokinetic (EK) solution 320 (depicted as upwardly pointing chevrons). The integrated EK engine and infusion module 306 also includes an infusion module housing 322, a movable partition 324, an infusion reservoir 326, an infusion reservoir outlet 328, and an infusion liquid 330 (depicted as dotted shading).

The moveable partition 324 can have a variety of configurations, but in the illustrated embodiment can include a first infusion seal 348, a spacer 349, and a second infusion seal 350. The spacer 349 is positioned between the first and second infusion seals 348, 350, with the first infusion seal positioned proximal of the spacer 349 and the second infusion seal 350 positioned distal of the spacer 349. The spacer 349 of the moveable partition 324 is at a position B in the first dispense state a shown in FIG. 4, and is at a position C in the second dispense state as shown in FIG. 5. The distance between position B and position C is labeled D in FIG. 5.

In an exemplary embodiment, the capacitive displacement position sensor 307 includes a first capacitive element 352, such as a capacitive plate, a second capacitive element 354, such as a capacitive plate, a first electrical contact 356, a second electrical contact 358, and a capacitance measurement module 360.

The first capacitive plate 352 is mounted on the movable partition 324, and moves parallel to the longitudinal axis of the infusion module housing 322 along with the movable partition 324. The second capacitive plate 354 remains stationary and is mounted on the infusion module housing 322 such that there is a gap G (also referred to as a separation) between the first capacitive plate 352 and the second capacitive plate 354. The gap G can be filled with any suitable material including, for example, air, a wall of the infusion module housing 322 (which is formed of plastic or other suitable electrically insulating material), other suitable electrically insulating material, and combinations thereof.

The first electrical contact 356 provides electrical contact between the first capacitive plate 352 and the capacitance measurement module 360, while second electrical contact 358 provides electrical contact between second capacitive plate 354 and capacitance measurement module 360. In the first dispense state depicted in FIGS. 4 and 6, the moveable partition 324 is in a first position, and the first capacitive plate 352 partially overlaps the second capacitive plate 354. The capacitance measurement module 360 is configured to provide a feedback signal FB to the closed loop controller 304 which is indicative of the capacitance between the first and second capacitive plates 352, 354. As the moveable partition 324 and the first capacitive plate 354 move and the capacitance between the first and second capacitive plates 352, 354 changes, the closed loop controller 304 uses the feedback signal FB to control the dispense state, as will be described in more detail below.

As the capacitance between two capacitive plates is proportional to their overlapping area divided by the distance between the plates, a measured capacitance between the first capacitive plate 352 and the second capacitive plate 354 can be readily correlated to the extent of their overlap. Since the first capacitive plate 352 is attached to the moveable partition 324, the extent of overlap and/or any change in overlap can be employed to determine the position (i.e., displacement position) of the moveable partition 324. For example, in FIGS. 5 and 7, the moveable partition 324 has moved relative to its position in FIGS. 4 and 6, and the overlap between the first capacitive plate 352 and the second capacitive plate 354 has increased. This increase in overlap will result in an increase in the capacitance that is measured by the capacitance measurement module 360.

The position of the movable partition 324 can then be readily derived from the change in capacitance between the two capacitive plates 352, 354 since the measured capacitance C is proportional to A/G where A is the area of plate overlap and G is the gap dimension. In this regard, the first and second capacitive plates 352, 354 have typical dimensions, for example, of 10 mm (width) by 20 mm (length). The area of overlap between the first and second capacitive plates 352, 354 can vary depending on the placement of the first and second capacitive plates 352, 354 on the moveable partition 324 and the infusion module housing 322. For example, the largest overlap between the first and second capacitive plates 352, 354 can be a substantially complete overlap of the first and second capacitive plates 352, 354, and the smallest overlap between the first and second capacitive plates 352, 354 has typical dimensions, for example, of 10 mm (in width) by 5 mm (in length). In addition, the gap dimension G can have a range between 10 and 1000 micrometers, and, for example, it can be 0.5 mm.

In the embodiments shown in FIGS. 4-7, both the first and second capacitive plates 352, 354 are in direct electrical connection with the capacitance measurement module 360. However, providing a direct electrical connection to the first capacitive plate 352 can raise the cost and complexity of manufacturing. FIG. 8 is a perspective depiction of a portion of an electrokinetic (EK) infusion pump 400 according to another embodiment of the present invention in a first dispense state. As is explained in more detail below, the EK infusion pump 400 employs a dual capacitive coupling configuration to address the issue of manufacturing cost and complexity. FIG. 9 is a perspective depiction of the portion of the EK infusion pump 400 in a second dispense state. FIGS. 8 and 9 are simplified in a similar manner to the simplified depictions of FIGS. 6 and 7.

FIG. 10 is a schematic drawing depicting a capacitive plate configuration 500 of the first dispense state of FIG. 8, while FIG. 11 is a schematic drawing depicting a capacitive plate configuration 600 of the second dispense state of FIG. 9.

Referring to FIGS. 8-11, the EK infusion pump 400 includes an integrated electrokinetic (EK) engine and infusion module 406, and a dual capacitive displacement sensor 407. The integrated EK engine and infusion module 406 includes an infusion module housing 422 and a moveable partition 424.

The dual capacitive displacement sensor 407 includes a first capacitive plate 482, a second capacitive plate 484 (configured as an extension of first capacitive plate 482), a third capacitive plate 486, a fourth capacitive plate 488, a first electrical contact 490, and a second electrical contact 492.

The first and second capacitive plates 482, 484 are mounted on the movable partition 424, and move parallel to the longitudinal axis of the infusion module housing 422 together with the movable partition 424 (for example, in the direction of arrow A6 as shown in FIG. 11). The third and fourth capacitive plates 486, 488 are mounted on the infusion module housing 422 such that there is a gap between the first capacitive plate 482 and the third capacitive plate 486, as well as a gap between the second capacitive plate 484 and the fourth capacitive plate 488. The gaps can be filled with any suitable material including, for example, air, a wall of the infusion module housing 422 (which is formed of plastic or other suitable electrically insulating material), other suitable electrically insulating material, and combinations thereof.

The first electrical contact 490 provides electrical contact between the fourth capacitive plate 488 and the capacitance measurement module 460, while the second electrical contact 492 provides electrical contact between the third capacitive plate 486 and the capacitance measurement module 460.

The extent of overlap between the first capacitive plate 482 and the third capacitive plate 486 is variable as the moveable partition 424 moves, as evidenced by a comparison of FIGS. 8 and 9 or FIGS. 10 and 11. However, the extent of overlap between the second capacitive plate 484 and the fourth capacitive plate 488 is constant as moveable partition 424 moves, as evidenced by a comparison of FIGS. 8 and 9 or FIGS. 10 and 11. The position of the movable partition 424 can then be derived from a change in capacitance as measured by the capacitance measurement module 460. The position of the moveable partition 424 can be readily derived since the total measured capacitance is the result of two capacitances in series, of which one is constant and one is variable with moveable partition position. In other words, 1/C_(tot) is equal to the sum of 1/C_(c) and 1/C_(v) (where C_(tot) is the measured total capacitance, C_(c) is the constant capacitance between the second and fourth capacitive plates 484, 488 and C_(v) is the variable capacitance between first and third capacitive plates 482, 486).

FIG. 12 is an electrical circuit schematic depicting an electric circuit 700 that is essentially equivalent to the circuit formed by the capacitive plates depicted in FIGS. 8-11. As depicted in FIG. 12, the circuit includes one variable capacitor that includes the first and third capacitive plates (i.e., capacitive plates 482 and 486) and one fixed capacitor that includes the second and third capacitive plates (i.e., capacitive plates 484 and 488).

FIG. 13 is a flow diagram illustrating a method 800 for the closed loop control of an electrokinetic (EK) infusion pump according to an exemplary embodiment of the present invention. The method 800 includes, at step 810, sensing a dispensing state of an EK infusion pump with a capacitive displacement position sensor. The capacitive displacement position sensor and the EK infusion pump can be any such sensor and EK infusion pump as described herein with respect to embodiments of the present invention.

Subsequently, the sensed dispensing state of the EK infusion pump is signaled to a closed loop controller via a feedback signal, as set forth in step 820. The closed loop controller then determines the dispensing state of the electrokinetic infusion pump based on the feedback signal, as set forth in step 830.

Subsequently, at step 840, the dispensing state of the EK infusion pump (e.g., infusion liquid displacement rate) is controlled by the closed loop controller by the sending command signals from the closed loop controller to an electrokinetic engine of the EK infusion pump. The command signal can be, for example, based on a comparison of the determined dispensing state and a predetermined desired dispensing state and be a command signal that adjusts for any differences between the determined dispensing state and the predetermined desired dispensing state.

The method 800 can be practiced using EK infusion pump systems according to the present invention including the embodiments of FIGS. 1-12. Moreover, steps 810 through 840 can be repeated as necessary to establish and maintain accurate control of the EK infusion pump dispensing state.

EK infusion pumps and EK infusion pump systems according to embodiments of the present invention are economical to manufacture since the capacitive plates of their capacitive displacement position sensors can be formed using conventional economical techniques such as laser ablation of thin metal layers, screen printing and offset printing. Moreover, since the plates can be manufactured economically, the capacitive displacement position sensors described herein can be included as a component within a disposable EK infusion pump.

In addition, capacitance can be measured using techniques with beneficially low power consumption, thus enabling EK infusion pumps and EK infusion systems with extended lifetimes. For example, capacitance-to-digital converter device AD7745 (commercially available from Analog Devices Inc., U.S.A.) can directly measure capacitance and convert the measured capacitance to a digital signal at an indicated power consumption of approximately 1 mW.

It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods within the scope of these claims and their equivalents be covered thereby

One skilled in the art will appreciate further features and advantages of the invention based on the above-described embodiments. Accordingly, the invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety. 

1. An electrokinetic infusion pump comprising: an infusion pump module; and an electrokinetic engine, wherein the infusion pump module includes a capacitive displacement position sensor configured for sensing a dispensing state of the infusion pump module.
 2. The electrokinetic infusion pump of claim 1, wherein: the infusion pump module includes an infusion module housing; the electrokinetic engine includes a moveable partition; and the capacitive displacement sensor includes a first capacitive plate disposed on the moveable partition and a second capacitive plate disposed on the infusion module housing.
 3. The electrokinetic infusion pump of claim 2, wherein the first capacitive plate and the second capacitive plate each have a width of approximately 10 mm and a length of approximately 20 mm.
 4. The electrokinetic infusion pump of claim 3, wherein a gap between the first capacitive plate and the second capacitive plate has a dimension in the range of approximately 10-1000 micrometer.
 5. The electrokinetic infusion pump of claim 2, wherein the capacitive displacement sensor is configured for measuring capacitance between the first capacitive plate and the second capacitive plate.
 6. The electrokinetic infusion pump of claim 1, wherein the electrokinetic engine includes a moveable partition and the infusion pump includes an infusion housing, and wherein the capacitive displacement sensor is a dual capacitive displacement sensor that includes: a first capacitive plate and a second capacitive plate disposed on the moveable partition; and a third capacitive plate and a fourth capacitive plate disposed on the infusion housing; wherein the first capacitive plate, the second capacitive plate, the third capacitive plate and the fourth capacitive plate are in operative electrical contact and wherein an overlap between the second and fourth capacitive plate is constant and an overlap between the first capacitive plate and the third capacitive plate is dependent on a position of the moveable partition.
 7. The electrokinetic infusion pump of claim 1, wherein the capacitive displacement sensor is configured to send a feedback signal to a closed loop controller, the feedback signal indicative of the capacitance between the first and second capacitive plates.
 8. The electrokinetic infusion pump of claim 1, wherein the infusion pump is configured to dispense an insulin containing infusion liquid.
 9. An infusion pump system, comprising: an infusion pump that includes: a capacitive displacement position sensor; and a closed loop controller, wherein the infusion pump and closed loop controller are in operative communication and configured such that the closed loop controller can determine and control a dispensing state of the infusion pump based on a feedback signal received from the capacitive displacement position sensor.
 10. The system of claim 9, wherein the infusion pump is an electrokinetic pump.
 11. The system of claim 10, wherein the electrokinetic infusion pump further includes an infusion pump module; and an electrokinetic engine, and wherein the capacitive displacement sensor is configured for sensing a dispensing state of the infusion pump module.
 12. The system of claim 11, wherein: the infusion pump module includes an infusion module housing; the electrokinetic engine includes a moveable partition; and the capacitive displacement sensor includes a first capacitive plate disposed on the moveable partition and a second capacitive plate disposed on the infusion module housing.
 13. The system of claim 12, wherein the capacitive displacement sensor is configured for sensing a dispensing state by measuring capacitance between the first capacitive plate and the second capacitive plate.
 14. The system of claim 13, wherein the first capacitive plate and the second capacitive plate each have a width of approximately 10 mm and a length of approximately 20 mm.
 15. The system of claim 14, wherein a gap between the first capacitive plate and the second capacitive plate has a dimension in the range of approximately 10-1000 micrometer.
 16. The system of claim 11, wherein the electrokinetic engine includes a moveable partition and wherein the capacitive displacement sensor is a dual capacitive displacement sensor that includes: a first capacitive plate; a second capacitive plate; a third capacitive plate; and a fourth capacitive plate, and wherein the first capacitive plate, the second capacitive plate, the third capacitive plate and the fourth capacitive plate are in operative electrical contact and wherein an overlap between the second and fourth capacitive plate is constant and an overlap between the first capacitive plate and the third capacitive plate is dependent on a position of the moveable partition.
 17. The system of claim 11, wherein the electrokinetic engine includes an electrokinetic supply reservoir that is at least partially collapsible.
 18. The system of claim 9, wherein the capacitive displacement sensor is configured to send the feedback signal to the closed loop controller.
 19. The system of claim 9, wherein the infusion pump is configured to dispense an insulin-containing infusion liquid.
 20. A method for the closed loop control of an infusion pump, comprising: sensing a dispensing state of an infusion pump with a capacitive displacement position sensor; signaling the sensed dispensing state of the infusion pump to a closed loop controller via a feedback signal; determining, with the closed loop controller, the dispensing state of the infusion pump based feedback signal; and controlling the dispensing state of the infusion pump with the closed loop controller by sending command signals from the closed loop controller to an engine driving the infusion pump. 